How can I read and write to the standard input, output and error streams stdin
, stdout
and stderr
in Fortran? I've heard writing to stderr
, for example, used to be write(5, fmt=...)
, with 5
the unit for stderr
, and I know the way to write to stdout
is to use write(*, fmt=...)
.
How do I read and write to the standard input and output units with the ifort
compiler?
Compiler version:
Intel(R) Fortran Compiler for applications running on Intel(R) 64, Version 10.0 Build 20070426 Package ID: l_fc_p_10.0.023 Copyright (C) 1985-2007 Intel Corporation. All rights reserved
If you have a Fortran 2003 compiler, the intrinsic module iso_fortran_env
defines the variables input_unit
, output_unit
and error_unit
which point to standard in, standard out and standard error respectively.
I tend to use something like
#ifdef f2003
use, intrinsic :: iso_fortran_env, only : stdin=>input_unit, &
stdout=>output_unit, &
stderr=>error_unit
#else
#define stdin 5
#define stdout 6
#define stderr 0
#endif
in my input/output routines. Although this of course means preprocessing your source file (to do this with ifort
, use the -fpp
flag when compiling your source code or change the source file extension from .f
to .F
or from .f90
to .F90
).
An alternative to this would be to write your own, non-intrinsic, iso_fortran_env
module (if you don't have a Fortran 2003 compiler), as discussed here (this link has died since this answer was posted). In this example they use a module:
module iso_fortran_env
! Nonintrinsic version for Lahey/Fujitsu Fortran for Linux.
! See Subclause 13.8.2 of the Fortran 2003 standard.
implicit NONE
public
integer, parameter :: Character_Storage_Size = 8
integer, parameter :: Error_Unit = 0
integer, parameter :: File_Storage_Size = 8
integer, parameter :: Input_Unit = 5
integer, parameter :: IOSTAT_END = -1
integer, parameter :: IOSTAT_EOR = -2
integer, parameter :: Numeric_Storage_Size = 32
integer, parameter :: Output_Unit = 6
end module iso_fortran_env
As noted in other answers, 0, 5 and 6 are usually stderr
, stdin
and stdout
(this is true for ifort
on Linux) but this is not defined by the Fortran standard. Using the iso_fortran_env
module is the correct way to portably write to these units.